Vehicle evaporative emissions control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations in a fuel vapor canister containing a suitable adsorbent, and then purge the stored vapors during a subsequent engine operation. The stored vapors may be routed to an engine intake for combustion, further improving fuel economy.
In a typical canister purge operation, a canister purge valve coupled between the engine intake and the fuel canister is opened, allowing for intake manifold vacuum to be applied to the fuel canister. On a boosted engine, that vacuum draw may be supplied via an ejector during boosted operation. For particular hybrid vehicles, that vacuum draw may be provided via a canister purge pump positioned between the canister and the canister purge valve, for example. Simultaneously, a canister vent valve coupled between the fuel canister and atmosphere is opened, allowing for fresh air to enter the canister. Further, in some examples a vapor blocking valve coupled between the fuel tank and the fuel canister is closed to prevent the flow of fuel vapors from the fuel tank to the engine. This configuration facilitates desorption of stored fuel vapors from the adsorbent material in the canister, regenerating the adsorbent material for further fuel vapor adsorption.
A flow map stored at a controller of a vehicle may be used to command an appropriate duty cycle for the canister purge valve when purging of the canister is requested. More specifically, a particular flow value may be commanded in response to a request to purge the canister, and a 3D flow map stored at the controller may be queried to determine an appropriate duty cycle for the canister purge valve as a function of engine manifold vacuum. Such a flow value may be chosen so as to avoid potentially stalling the engine due to a rich amount of fuel vapors emanating from the canister (and fuel tank in some examples), and may be further based on a number of other relevant engine operating parameters. Furthermore, it is desirable to learn canister loading state via feedback from exhaust gas oxygen sensors during purging operations, and in order to accurately learn such a loading state, it is imperative that the commanded flow is accurate.
Degradation of components of the evaporative emissions system may adversely impact purging of the canister. For example, flow maps used to control a canister purge valve duty cycle for purging may not be accurate in the presence of degradation. Thus, it is desirable to regularly perform onboard methodology to indicate a level to which the evaporative emissions system and its components may be degraded, such that onboard strategy may update such flow maps. For hybrid vehicles with limited engine run time, it is desirable to perform such methodology to indicate the level to which the evaporative emissions system and its components are degraded, while the engine is not combusting air and fuel. The inventors have herein recognized the above-mentioned issues, and have developed methods and systems to address them. In one example, a method comprises during a condition where an engine of a vehicle is not combusting air and fuel, applying a pressure from an evaporative emissions system of the vehicle to an intake of the engine, and indicating an absence of degradation in the evaporative emissions system based on a test flow in the intake of the engine being within a predetermined threshold of a baseline flow obtained at an earlier time via applying the pressure. In this way, a presence or absence evaporative emissions system degradation may be indicated in the absence of engine operation.
As one example, a purge valve positioned in a purge line between the fuel vapor storage canister and the engine is commanded fully open, and wherein a throttle positioned in the intake is commanded fully open for obtaining the test flow and the baseline flow, for applying the pressure. Furthermore, applying the pressure may include applying a positive pressure, or may include applying a negative pressure. Applying the negative pressure may include utilizing a pump positioned in a vent line of the evaporative emissions system is controlled to a predetermined speed for applying the negative pressure to obtain the test flow and the baseline flow. Applying the positive pressure may include routing pressure generated during a refueling event of a fuel tank of the vehicle to the intake.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.